1. Field of the Invention
The present invention relates to a method and to a device for an address-free fault location by means of loop closure for a message transmission link from a locating end station via at least one intermediate station which regenerates and/or amplifies the transmission signals in both transmission directions which intermediate station contains a loop closure switch for the connection of the output of the intermediate station for the one transmission direction with its input for the other transmission direction.
2. Description of the Prior Art
Cable links for the transmission of carrier-frequency or digital signals contain intermediate stations which are inserted at specific spacings into the transmission link, in which intermediate stations the transmitted signal is regenerated and/or amplified. Even the light wave-guide transmission systems which have recently arisen require regenerating and amplifying intermediate stations at specific spacings because of the attenuation and distortion characteristics of the light guides which are used. These intermediate stations thereby correspond to the intermediate stations for copper cable, only an optical signal receiver is preconnected and an optical transmitter is postconnected. The intermediate stations are thus, as a rule, inserted such that amplifiers and regenerators for the one conversation direction are housed with those for the other conversation direction together in a common housing. The other end station is thereby equipped just like the intermediate station and it can also be located. This common housing makes possible the loop closure, wherein, in the intermediate station, a connection is made from the regenerator and amplifier device for the one transmission direction with the regenerator and amplifier device for the other transmission direction and, via this connection, a test signal which is sent out from the locating end station is returned. The loop closure can thereby be released by means of the transmission of a specific address in an intermediate station which recognizes this address. There are also known, for example from the German Patent Application No. P 2,653,201.4, address-free fault locating methods in the case of which, by means of the transmission of specific preparation and loop closure signals, a loop closure is produced, and by means of short duration interruption of the transmission of the loop closure commands, the connecting further of the loop closure is brought about to the next intermediate station. The loop closure is thereby not controllable simultaneously from both end stations; however, in general, this is also not practical.
In the case of loop closures of this sort, with respect to the unambiguous assignment of recognized faults, it is important that, if possible, all components which are important for the signal transmission in the intermediate station are connected into the loop closure path and tested. This applies in particular for those optical transmitters and receivers in light wave-guide transmission systems which are susceptible to alteration and interference. With respect to the complete testing of all components, the loop closures should therefore proceed from the transmitting end stage of the one transmission direction to the receiving input of the other transmission direction. In the case of copper cables, there hereby results the difficulty that between the transmitter end stage and the transmission cable, a separating switch must be provided which, on the one hand, must be suited for the switching of comparatively high powers and, on the other hand, must be capable of switching signals of comparatively high frequency. In the case of light wave-guide transmission systems, such optically functioning operating switches which have high reliability are not known at this time, so that the solution does not readily exist for light wave-guide transmission systems.